MXene/SnS2 Heterojunction for Detecting Sub-ppm NH3 at Room Temperature

Detection of ultralow concentrations of ammonia is very important in many applications such as fishing, poultry, agriculture, industry, biomedicine, and clinical diagnosis. However, detecting sub-ppm NH3 remains a challenge for chemiresistive-type gas sensors. Two-dimensional (2D) materials display tremendous potential for effective gas detectors that can be used in these applications. The as-developed MXene/SnS2 heterojunction-based chemiresistive-type sensor presents superior gas-sensing performance toward sub-ppm ammonia at room temperature. The sensor can detect NH3 concentrations down to 10 ppb at room temperature. It also displays excellent long-term stability, with a decline in the response at ∼3.4% for 20 days. The developed sensor also displays good selectivity toward NH3 relative to some potential interferents, such as HCHO, C2H5OH, CH3OH, C3H6O, benzene, and NO2. The measured in situ diffuse-reflectance infrared Fourier transform (DRIFT) spectra confirm that the products of nitric oxides during the chemical reactions occurred at the surface of MXene/SnS2. Density functional theory (DFT) based on the first principles was implemented to compute the adsorption ability of NH3 at the surface of the MXene/SnS2 heterostructure. This indicates that the enhancement in the sensing properties of the MXene/SnS2 heterostructure-based chemosensor could be ascribed to the stronger NH3 adsorption, better catalytical activity, and more effective charge transfer bestowed by the formed heterostructure and the electron-redistribution-assisted stronger extraction of electrons from the sensing material.